Enyne Cycloisomerization and Related Reactions

Another subfield of enyne cycloisomerization chemistry is best described as cycloaddition reactions. For instance, allenedienes were found to react smoothly in the presence of an IPr-based gold(I) cationic species to produce the formal [4 + 3] cycloadducts (Equation (11.8)). This method is a valuable approach to fused seven-membered ring systems and was applied to a transannular reaction, allowing for the construction of a pentacyclic system. Of note, Toste showed that, by replacing the NHC on gold by a triarylphosphite, an alternative [4 + 2] cycloaddition was observed from the same linear allenedienes.  

Even though not strictly speaking belonging to enyne cycloisomerization, an alkyne and an alkene can react intermolecularly with each other provided the alkyne is properly activated. Zhang and co-workers reported a number of such cycloadditions where a gold-mediated cascade was initiated by carbonyl addition to the alkyne moiety. The resulting 1,4- or 1,3-dipoles could then participate to formal [4 + 2] and [3 + 2] cycloadditions with an olefinic partner, giving access to 

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